This invention relates generally to laser-based additive manufacturing and, in particular, to direct-metal deposition, or DMD. More specifically, this invention relates to the production of overhang, undercut, and cavity structures using DMD processes.
U.S. patent application Ser. No. 09/526,631 relates to the production of smart dies and molds using a direct metal deposition or DMD process. This parent application describes how DMD may advantageously be employed to integrate sensors into dies, molds, and other articles for monitoring temperature, distortion and/or stress. This previous patent application also illustrates the ability of the DMD method to create complex and multi-material three-dimensional articles with built-in cooling channels and pipes.
The ability to build overhang and undercut features and, in particular, three-dimensional cooling channels in injection die-casting molds, is an important aspect of rapid prototyping. Moreover the ability and flexibility to deposit material in desired locations with DMD to build complicated 3D parts, as well as in-situ 3D channels, adds numerous advantages to the process. With the help of appropriate software to analyze heat transfer phenomena, nearly ideal articles may be manufactured using DMD. Such parts offer highly effective heat transfer while avoiding temperature gradients through uniform cooling made possible in part by channels, pipes, or other three-dimensional structures.
This invention provides further details with respect to the fabrication of overhang, undercut, and cavity structures using laser-aided direct-metal deposition (DMD) processes. Important characteristics of the DMD method include the ability to control the height of the deposited layer from the melt pool for each pass of the laser beam through a feedback controller coupled with optoelectric sensors. The thickness of the deposited layers can be as small as a couple of hundred microns, and the final surface roughness is less than that.
According to the invention, cooling channels and other features, which are part of the geometry or structure of the article, including holes, cavities, discontinuities, steps, corners, and so forth, are created during the same DMD fabrication process. In the preferred embodiment, this is accomplished through the selective deposition of a lower melting point sacrificial material. In one disclosed example, aluminum is used as a sacrificial material in conjunction with the fabrication of a steel body. Other materials and material combinations, including copper-tin alloys, are also disclosed.
Following the integrated deposition of both materials using DMD, the part is soaked in a furnace at a temperature sufficiently high to melt out the sacrificial material. As preferred options, the heating is performed in an inert gas environment to minimize oxidation, with a gas spray also being used to blow out remaining deposits.
Using this technique, articles having integral sensors and cooling channels may be used as part of an automated system for controlling the temperature, stress and strain during the shaping or forming of a product using the resultant smart die or mold. Such a system would preferably include means of controlling the inlet flow of coolant and means for controlling or terminating the forming or injection process. The control is preferably mediated through a computer which analyzes and evaluates the inputs from the sensors and transmits the resulting information to a flow controller and to a process controller or logic gate, so that appropriate actions are carried out on a continuous basis.